The present invention relates to a method for producing ethanol from lignocellulose-containing raw materials.
Among the process options for producing ethanol from lignocellulosic substrates (e.g., trees, grasses, and solid wastes) are those known as Direct Microbial Conversion ("DMC") and Simultaneous Saccharification and Fermentation ("SSF"). In the DMC method, a single microbial system both produces cellulase enzyme and produces ethanol as a fermentation product. The SSF method utilizes, two microbial systems, one of which produces cellulase enzyme and the other of which carries out the fermentation process to produce ethanol.
Biologically-mediated process steps are the most costly and the least developed in current designs for ethanol production. Typical ethanol production methods for lignocellulosic substrates require very long reaction times (e.g., about one week), and hence the bioreactors used in the process must have very large volumes for a given rate of throughput. As a result the bioreactor in which solids conversion takes place is a key cost component.
Accordingly, there is a need for a method of producing ethanol from cellulosic substrates using bioreactors characterized by higher volumetric productivity (rate of throughput per unit volume), and at a lower production cost.
It is thus an object of the invention to provide a method of producing ethanol from lignocellulosic substrates in an economically feasible manner. A further object of the invention is to provide a bioreactor suitable for carrying out such a method of producing ethanol from lignocellulosic substrates. Another object of the invention is to provide a bioreactor for the production of ethanol from organic substrates which possesses a high volumetric productivity. It is also an object of the invention to provide a method, and a suitable bioreactor, useful for the large-scale production of ethanol from lignocellulosic substrates. Other objects of the invention will be apparent to those of ordinary skill in the art upon reading the disclosure which follows.